1. Field of the Invention
The present invention relates to a technique for coating surfaces with bitumen based mixtures, particularly for road surfaces and in particular mixtures for coating gravel.
2. Description of the Background
The bitumens used for surface coating to render them water-tight as in the case of terraces or on surfaces on which vehicles run, i.e., particularly roadways, when it is necessary to provide a road surface with a water impermeable layer by using a pervious bitumen bound stone, are almost never used in the pure state. Indeed, their high and low temperature performance is inadequate and, by themselves, they provide surfaces which are fragile, which break down under frost conditions and which, in contrast, become soft when exposed to heat. In order to improve the behavior of the bitumens and above all the coating materials and in order thus to widen the range of temperatures in which they can be used, various substances are added to the bitumen, from the most banal such as crushed powdered lime, to the most sophisticated such as styrene-butadiene-styrene based macromolecules. Inter alia, a well-known alternative is to add various quantities of fibrous materials such as asbestos, rock fibers or glass fibers to bitumen. These additives widen the range of temperatures over which the bituminous mixtures may be used. However, the use of such mixtures for the production of drainage coatings in which one seeks to limit crushing under load at high temperature remains inadequate, i.e., only uses under low loading and/or at limited temperature are possible. Under a heavy loading or under considerable heat, the bitumen flows and the interstices between the gravel become obstructed, and then drainage is no longer feasible through the surfacing of the roadway.
Specific disclosures of the incorporation of mineral fibers into bitumen, include for example, Swedish Patent Se 211 163, which discloses the use of a filler, in bitumen, which is mineral fibers having a mean diameter of between 5 and 10 .mu.m with lengths of between 0.1 and 5 mm. By contrast, more recently, European Patents EP 55 233 and EP 58 290 have disclosed the use of fibers having a mean diameter of 1 to 5 .mu.m, which are treated with a cationic wetting agent under particular mixing conditions.
A need continues to exist for a bitumen based mixture of improved properties for coating surfaces.